Photolithography is conventionally used in the fabrication of semiconductor devices. It is typically performed using a device called a photolithography track. An important aspect of photolithography is the development of the photoresist. The dimensions of the photoresist pattern is important in the fabrication of semiconductor device since an etch or implantation of the substrate is performed based upon the photoresist pattern. The photoresist is patterned by a mask. The masked photoresist is then exposed to light from a light source. After exposure, developer is applied to remove the mask and exposed portions of the photoresist, leaving a patterned photoresist behind. The developer is typically a base and water mixture. Photolithography is well known in the art and will not be discussed in detail here.
FIG. 1 illustrates a portion of a conventional photolithography track. The track 100 includes a wafer 102 which may be spun by a chuck and motor 104. While the wafer 102 is spinning, a developer dispenser 106 equipped with a nozzle 108 moves over the spinning wafer 102 and applies an amount of developer to remove the mask and exposed portions of the photoresist, as described above. The dispenser 106 then moves back and rests in a nozzle block 110 which protects the nozzle 108 when the dispenser 106 is not in use. A drain pipe 112 is coupled to the nozzle block 110 for draining any excess developer from the nozzle block 110.
An important parameter in controlling the dimensions and shape of the patterned photoresist is the amount of developer applied. The amount may be determined from the flow rate and application time of the developer. However, it is often more accurate to measure the volume of the developer dispensed from the nozzle 108. A conventional method of performing this volume check involves dispensing the developer at the point of use into a container and then transferring the developer from this container to a volume measuring apparatus. Because the location of the nozzle 108 in the track 100, there is often little room to place a container under the nozzle 108 so that it can catch the developer which is dispersed. Even when a container can be so placed, there is typically some spillage of developer when it is transferred from the container to the measuring apparatus. The spilled developer may then contact parts of the track 100, such as electronic circuitry and wiring, which can lead to corrosion and/or premature failure of those parts. The spilled developer may also results in an inaccurately low volume measurement.
Accordingly, what is needed is an improved method and system for measuring fluid volume in a photolithography track. The method and system should provide a more accurate measurement of developer volume. The present invention addresses such a need.